Electrostatic writing means



June 9, 1964 J STONE, JR 3,136,917

ELECTROSTATIC WRITING MEANS Filed March 14. 1960 //VTEA/5/7Y DEFLECT/O/V FIG 1 CONTROL SIG/VAL SIGNAL SOURCE SOURCE :llJlllllk J:

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INVENTOR. Joseph James Sta/1M United States Patent 3,136,917 ELECTROSTATIC WRITING MEANS Joseph James Stone, Jr., Glenview, Ill., assignor to A. B. Dick Company, Niles, Ill., a corporation of Illinois Filed Mar. 14, 15960, Ser. No. 14,687 4 Claims. (Cl. 31512) This invention relates in general to an improved electrostatic printing arrangement, and more particularly to an arrangement for improving the resolution of images secured by means of electrostatic printing tubes.

In known electrostatic printing arrangements such as that disclosed in an application by John S. Tregay, Jr., filed May 10, 1957, Serial No. 658,275, a conventional cathode ray tube is modified by the provision of an array of wires in its face, which extend from the interior surface of the face to the exterior surface. A high voltage beam of electrons is varied in accordance with a desired image and traverses the interior terminations of the array of wires embedded in the non-conductive face of the tube to cause a discharge through a dielectric or printing paper passing adjacent to the exterior wire terminations at a desired speed. This arrangement although producing satisfactory images does give rise to some difiiculties in resolution due to the capacitive effect of the wires in the matrix.

Thus the dielectric is located between the Wires and an exterior electrode maintained at ground or anode potential, while the respective wires are charged toward the cathode potential. This creates a charged condition therebetween which is satisfied only by discharge through the dielectric, and on initiation of the discharge, it continues until complete. If the discharge period is extended, it may result in poor definition of the discharge area marked on the dielectric.

In addition, the high beam currents produce considerably secondary emission which must be controlled in order to secure good reliable image resolution.

It is, therefore, proposed by the present invention to coat the interior surface of the tube with a dielectric coating which prevents any secondary electrons from striking or contacting the Wires, but at the same time permits the passage of the high energy beam. In addition, by applying a thin conductive layer to the dielectric coating and biasing the same, the secondary electrons emitted as a result of beam passage through the dielectric are collected to prevent them affecting image resolutions.

Accordingly, it is an object of the present invention to provide an electrostatic printing tube having improved image resolution.

It is another object of the present invention to provide an electrostatic printing tube in which secondary emission is prevented from interfering with the image.

The features of this invention include the coating of the inner surface of the face plate with a dielectric which is only penetrated by high beam current and the provision of a biased conductive layer on the coating to dissipate the secondary emission effects caused by the beam passage.

These and other objects, features and advantages of this invention will become apparent on reading the following specification and claims in conjunction with the drawings of which:

FIG. 1 is a standard cathode ray tube of the type used in electrostatic printing modified in accordance with the invention.

FIG. 2 is a partial sectional view showing the manner in which the coatings are related to a wire conductor in the electrostatic printing tube.

Referring now to FIG. 1 showing a cross section of the electrostatic printing tube incorporating the principles "ice of the present invention, it will be seen that the tube indicated at 10 is similar to a conventional cathode ray tube. It includes an evacuated envelope 12, which carries a cathode 14, a control. grid 13 connected to a suitable signal source 15, an anode or accelerating electrode 16, a focus coil 18, and a deflection coil 20. The cathode is cimnected to the negative terminal of high voltage supp y 22.

The deflection coil 20 is controlled from a suitable deflection signal source 28, for controlling the beam produced at the cathode 14 while the beam is modulated by the signals from source 15 for reproducing an image represented by those signals.

In addition, the tube includes any well known type of face plate 32 of dielectric material in which the wires 34 are carried or embedded. Adjacent the terminations of the wires, exterior of the tube, a suitable dielectric material 36 is provided for recording the image. It is moved in the direction indicated by the arrow and has associated on its other side a conductor 38, at ground potential whereby discharge from the wires through the dielectric is accomplished.

On the inside of the tube 10 and adjacent the interior terminations of the wires 34 along the face plate 32 a dielectric coating 40 is provided as may best be seen in FIG. 2. The coating 40 may be formed by a deposit of aluminum which is fired in a properly controlled atmosphere to form an oxide. A thin conductive coating 44 is then deposited on the coating 40 and is extended to a suitable bias source such as ground. The selection of the bias is of course dependent on desired characteristics.

In operation, the primary beam is of course directed to the various wires 34, in accordance with the desired scanning rate, while the image reproducing dielectric 36 passes adjacent the external terminations of the wires.

The control grid 13 is controlled in accordance with the signals introduced thereto from signal source 15. These signals represent the object to be reproduced and modulate the beam emitted by 14 accordingly. The potential source 22 furnishes a voltage of sufficient magnitude to provide a primary beam which penetrates the layers or coatings 40 and 44 to charge the Wires 34 in accordance with the modulations introduced from signal source 15.

Stray electrons which are being emitted from the various components of the tube 10 are prevented from penetrating the layer 40 and therefore cannot affect image resolution. The secondary or stray electrons emitted as a result of the beam striking the interior terminations of wires 34 and the face plate 32 are collected along dielectric and conducted away by layer 44 to prevent a harmful charging effect of these electrons. Thus the effect of stray and secondary electrons on image resolution is reduced to provide improved image resolution.

In accordance with the above, there has been shown and described herein a novel, useful and simple arrangement for improving the operation of an electrostatic writing tube, but the particular embodiments or forms of the invention described herein are not limitations upon other manners of practicing the invention.

I claim:

1. An electrostatic printing tube in which a pluraltiy of conductive elements are successively scanned by a primary electron beam for recording on a dielectric, the improvement comprising a dielectric face plate in which said elements are carried in parallel and insulated one from the other, and a dielectric coating covering one surface of said face plate and which is penetrated only by said electron beam to charge said elements, in accordance with desired input signals.

2. The arrangement claimed in claim 1 in which a conductive coating is carried on the'inner surface of said di-.- electric coating for collecting secondary electrons caused by said beam. I V V 3. The arrangement claimed in claim 2 in which said conductive coating is thinner than said dielectric coating,

4. An electrostatic printing tube in'which a plurality of conductors extend from the interiorto the exterior surface of the dielectric face of the tube and are charged successively by a primary electron beam for enabling a discharge through a dielectric recording material for re-; producing an image, the improvement comprising an alu:

minum oxide coating over the interior surface'of said face and the interior terminations of said conductors and penetrable only by'said beam, ahd a thin'condiictivecoating over said oxide coating and connected to a suitable bias source for collecting secondary electrons emitted by; said a i beam striking saidplate and conductors.

References Cited inrthefile of this patent UNITED STATES PATENTS Borden Apr, 4, 1961' 

4. AN ELECTROSTATIC PRINTING TUBE IN WHICH A PLURALITY OF CONDUCTORS EXTEND FROM THE INTERIOR TO THE EXTERIOR SURFACE OF THE DIELECTRIC FACE OF THE TUBE AND ARE CHARGED SUCCESIVELY BY A PRIMARY ELECTRON BEAM FOR ENABLING A DISCHARGE THROUGH A DIELECTRIC RECORDING MATERIAL FOR REPRODUCING AN IMAGE, THE IMPROVEMENT COMPRISING AN ALUMINUM OXIDE COATING OVER THE INTERIOR SURFACE OF SAID FACE AND THE INTERIOR TERMINATIONS OF SAID CONDUCTORS AND PENETRABLE ONLY BY SAID BEAM, AND A THIN CONDUCTIVE COATING OVER SAID OXIDE COATING AND CONNECTED TO A SUITABLE BIAS SOURCE FOR COLLECTING SECONDARY ELECTRONS EMITTED BY SAID BEAM STIKING SAID PLATE AND CONDUCTORS. 